Musnad Ahmad 2:52

Mu'awiyah ibn 'Amr narrated to us, Za'idah narrated to us, 'Asim narrated to us. And Husayn ibn 'Ali [narrated] from Za'idah, from 'Asim, from Zirr, from 'Abdullah, who said: When the Messenger of Allah, peace and blessings of Allah be upon him, was taken [in death], the Ansar said: "An amir from us, and an amir from you." 'Umar came to them and said: "O assembly of the Ansar, do you not know that the Messenger of Allah, peace and blessings of Allah be upon him, commanded Abu Bakr to lead the people in prayer? So which of you finds it agreeable to himself to step forward before Abu Bakr?" The Ansar said: "We seek refuge in Allah from stepping forward before Abu Bakr."